1. Field of the Invention
The present invention relates a constant voltage circuit with excellent volt-ampere and temperature characteristics for regulating especially a low load voltage.
2. Description of the Prior Art
The Zener diodes, which are designed to positively utilize their Zener effect and avalanche breakdown, have been widely employed as voltage reference or constant-voltage devices. A reverse bias current is nearly constant until the reverse bias voltage reaches a critical voltage at which the reverse current is abruptly and markedly increased. In the breakdown region the voltage across a Zener diode remains nearly constant independently of wide variation in current flowing therethrough. This phenomenon is used to regulate the load voltage against variation in load current and against variation in supply voltage. However, the breakdown voltage of a Zener diode is generally higher than 6 V even though it is lower than a constant voltage regulated by a constant-voltage discharge tube or the like. As a result the constant voltage circuit employing a Zener diode for regulating a load voltage lower than the breakdown voltage of the Zener diode is complex in construction, expensive to fabricate and unstable and inaccurate in operation because of the unsatisfactory volt-ampere and temperature characteristics of a Zener diode used.
In general the electronic devices including electronic computers, which become more and more complex both in construction and operation, demand constant voltage devices which are extremely reliable, stable, and accurate in operation. Especially the electronic circuits consisting of ICs and LSIs require constant voltage circuits with an extremely small voltage fluctuation.